A digital subscriber line (DSL) is a high-speed data transmission technology for transmitting data over a phone twisted-pair cable, for example, an unshielded twisted pair (UTP). There are multiple DSL lines in a DSL system. Currently, a DSL access multiplexer (DSLAM, Digital Subscriber Line Access Multiplexer) is generally used to provide an access service for the multiple DSL lines. However, due to an electromagnetic induction principle, mutual crosstalk is generated between multiple signals that gain access to the DSLAM.
To eliminate the crosstalk, for example, a Vectored DSL technology may be used to eliminate far-end crosstalk, and for example, a TDD DSL technology may be used to eliminate near-end crosstalk. The Vectored DSL technology uses a feasibility of performing combined receiving and sending at the DSLAM end and uses a signal processing method, so as to offset the crosstalk. The time division duplexing (TDD) DSL technology is an orthogonal frequency division multiplexing (OFDM) modulation technology of the time division duplex, and when the DSL system is at a frequency up to 100 MHz, this technology can greatly reduce a difficulty in designing a hybrid circuit.
Currently, before multiple DSL lines send a data signal, the multiple DSL lines may be trained, for example, by sending a training signal, to eliminate crosstalk between the multiple DSL lines. Then, a data signal is sent over multiple trained DSL lines.
Once a DSL line is faulty, a SELT measurement signal is sent over the faulty DSL line so as to diagnose the faulty DSL line. However, continuously sent SELT measurement signals within a relatively wide spectrum range cause interference to a data signal transmitted over a neighboring DSL line, even lead to generation of a bit error on the neighboring DSL line, and result in a disconnection in a serious situation.
Therefore, how to reduce crosstalk to a data signal sent over another DSL line is an urgent problem to be resolved, where the crosstalk is caused by a SELT measurement signal sent over a DSL line on which a SELT diagnosis is being performed.